1. Field of the Invention
The invention relates to a travelling mechanism, especially for a lifting device such as a hoist.
2. Discussion of the Prior Art
U.S. Pat. No. 2,470,060 discloses a travelling mechanism that can be used, in particular, for lifting devices. This travelling mechanism comprises a rail that consists of flange parts and web parts. Two running wheels, which are located opposite to each other, roll on the flange inner sides of the rail. To guide the travelling mechanism, guide rollers rest in front of and behind each running wheel, on both sides, parallel to the web. The running wheels and the guide rollers are rotatably-mounted in lateral bars. The two bars are spaced relative to each other and connected to each other by means of a connecting element in the manner of a traverse. However, this travelling mechanism can be used only for a predetermined flange width. It is assembled completely prior to use and then placed on the travelling rail. A change in the distance between the two lateral bars and thus between the running wheels is not possible. This travelling mechanism thus can be used only in rail profile systems with a constant flange width, whereby an optimal distance is selected between the web and the running wheels to attain the desired statically advantageous stress on the travelling rail and the travelling mechanism.
From European reference EP 0 078 085 A1, another travelling mechanism is known, which comprises a travelling rail and running wheels. The wheels are located opposite to each other and rest on the flange parts of the travelling rail. Guide rollers are not provided in this travelling mechanism. To adjust to different web widths, the bilaterally arranged bars, in which the running wheels are rotatably-mounted, are adjustable with respect to their spacing. Seen in the direction of travel, connecting traverses equipped with slots are located in front of and behind the travelling rail. The slots run in pairs on both sides of the web at a right angle to the direction of travel. The connecting traverse is attached to the bars with screws, which are inserted through the slots. This makes it possible to adjust the distance between the two bars.
Due to the intrinsic weight of the trolley, the clearance between the wheel flange and the flange side can be adjusted only by great force. However, the crucial disadvantage of this travelling mechanism is that, although adjustment to different flange widths is possible, the running wheels are, in the case of wider flanges, farther from the web. This leads to known disadvantages: The travelling rail is unfavorably stressed, and the flange is subjected to higher bending stress, which results in a larger profile having to be used.